Recent Scientific Papers of Interest

Taishi Yoshii, Margaret Ahmad, Charlotte Helfrich-Forster

PLoS Biol 7(4): e1000086.doi:10.1371/journal.pbio.1000086

Abstract

Since 1960, magnetic fields have been discussed as Zeitgebers for circadian clocks, but the mechanism by which clocks
perceive and process magnetic information has remained unknown. Recently, the radical-pair model involving lightactivated
photoreceptors as magnetic field sensors has gained considerable support, and the blue-light photoreceptor
cryptochrome (CRY) has been proposed as a suitable molecule to mediate such magnetosensitivity. Since CRY is
expressed in the circadian clock neurons and acts as a critical photoreceptor of Drosophila’s clock, we aimed to test the
role of CRY in magnetosensitivity of the circadian clock. In response to light, CRY causes slowing of the clock,
ultimately leading to arrhythmic behavior. We expected that in the presence of applied magnetic fields, the impact of
CRY on clock rhythmicity should be altered. Furthermore, according to the radical-pair hypothesis this response should
be dependent on wavelength and on the field strength applied. We tested the effect of applied static magnetic fields
on the circadian clock and found that flies exposed to these fields indeed showed enhanced slowing of clock rhythms.
This effect was maximal at 300 lT, and reduced at both higher and lower field strengths. Clock response to magnetic
fields was present in blue light, but absent under red-light illumination, which does not activate CRY. Furthermore, cryb
and cryOUT mutants did not show any response, and flies overexpressing CRY in the clock neurons exhibited an
enhanced response to the field. We conclude that Drosophila’s circadian clock is sensitive to magnetic fields and that
this sensitivity depends on light activation of CRY and on the applied field strength, consistent with the radical pair
mechanism. CRY is widespread throughout biological systems and has been suggested as receptor for magnetic
compass orientation in migratory birds. The present data establish the circadian clock of Drosophila as a model system
for CRY-dependent magnetic sensitivity. Furthermore, given that CRY occurs in multiple tissues of Drosophila,
including those potentially implicated in fly orientation, future studies may yield insights that could be applicable to
the magnetic compass of migratory birds and even to potential magnetic field effects in humans.

Author Summary

Magnetic fields influence endogenous clocks controlling the sleep–wake cycle of animals, but the underyling mechanisms are unclear. Birds that can do magnetic compass orientation also depend on light, and the blue-light photopigment cryptochrome was proposed to act as a navigational magnetosensor. Here we tested the role of cryptochrome as a light-dependent magnetosensor of the clock in the fruit fly Drosophila melanogaster. In wild-type flies we found that constant magnetic fields slowed down the speed of the clock in a dose-dependent manner—but only in the presence of blue light. In mutants lacking functional cryptochrome, the magnetic fields had no significant effects on the endogenous clock, whereas the effects were enhanced after overexpression of cryptochrome. Our data suggest that cryptochrome works as a magnetosensor in the endogenous clock when it is excited by blue light. Our work
supports previous data showing that fruit flies need functional cryptochrome to perceive a magnetic field, demonstrating that the
interaction of cryptochome and magnetic fields are not just for the birds.

Leukemia & Lymphoma, December 2008; 49(12): 2344–2350

Abstract

A case-only study was conducted in 123 patients with sporadic acute leukemia (AL). The locations of electric transformers
and power lines were noted in each area, and their distances from the houses of the study patients were measured. The
intensities of magnetic fields (B) were measured in 66 cases. Unconditional logistic regression analysis was performed
adjusting for age, gender, parental education and occupation, indoor and outdoor pesticides use, presence of television sets,
refrigerators and microwave ovens in children’s rooms and the presence of chemical factories or telecommunication
transmitters within 500 m of the houses. The results of the gene–environment analyses revealed that an interaction existed
between the XRCC1 Ex9 + 16 A allele and the presence of electric transformers and power lines within 100 m (Mean
B = 0.14 µTeslas, µT) of the houses (interaction odds ratio, COR = 4.31, 95%CI: 1.54–12.08). The COR for the interaction
of XRCC1 Ex9 + 16A and the presence of these installations within 50 m (Mean B = 0.18 µT) of the houses was 4.39
(95%CI: 1.42–13.54). Our results suggest a possible association between electric transformers and power lines and the
XRCC1 Ex9 + 16A allele in patients with childhood AL.

Residence Near Power Lines and Mortality From Neurodegenerative Diseases:
Longitudinal Study of the Swiss Population

American Journal of Epidemiology Advance Access published November 5, 2008

Abstract

The relation between residential magnetic field exposure from power lines and mortality from neurodegenerative
conditions was analyzed among 4.7 million persons of the Swiss National Cohort (linking mortality and census
data), covering the period 2000–2005. Cox proportional hazard models were used to analyze the relation of living in
the proximity of 220–380 kV power lines and the risk of death from neurodegenerative diseases, with adjustment
for a range of potential confounders. Overall, the adjusted hazard ratio for Alzheimer’s disease in persons living
within 50 m of a 220–380 kV power line was 1.24 (95% confidence interval (CI): 0.80, 1.92) compared with persons
who lived at a distance of 600 m or more. There was a dose-response relation with respect to years of residence in
the immediate vicinity of power lines and Alzheimer’s disease: Persons living at least 5 years within 50 m had an
adjusted hazard ratio of 1.51 (95% CI: 0.91, 2.51), increasing to 1.78 (95% CI: 1.07, 2.96) with at least 10 years and
to 2.00 (95% CI: 1.21, 3.33) with at least 15 years. The pattern was similar for senile dementia. There was little
evidence for an increased risk of amyotrophic lateral sclerosis, Parkinson’s disease, or multiple sclerosis.

Ana M García, Antonio Sisternas, and Santiago Perez Hoyos

International Journal of Epidemiology 2008 37(2):329-340

Abstract

Background: Among potential environmental risk factors for Alzheimer disease (AD), occupational exposures have received some attention, including extremely low frequency electromagnetic fields (ELF-EMF). A systematic review and meta-analysis of published epidemiological studies on this subject was carried out.

Methods: The search was concluded in April 2006. Bibliographic databases consulted included PubMed, EMBASE, Cochrane Library and NIOSHTIC2. Pooled estimates were obtained using random-effects meta-analysis. Sources of heterogeneity between studies were explored, as was publication bias.

Conclusions: Available epidemiological evidence suggests an association between occupational exposure to ELF-EMF and AD. However, some limitations affecting the results from this meta-analysis should be considered. More information on relevant duration and time windows of exposure, on biological mechanisms for this potential association and on interactions between electromagnetic fields exposure and established risk factors for AD is needed.

PNAS, 2008, 105, 14395-14399

Abstract

One of the two principal hypotheses put forward to explain the
primary magnetoreception event underlying the magnetic compass
sense of migratory birds is based on a magnetically sensitive
chemical reaction. It has been proposed that a spin-correlated
radical pair is produced photochemically in a cryptochrome and
that the rates and yields of the subsequent chemical reactions
depend on the orientation of the protein in the Earth’s magnetic
field. The suitability of cryptochrome for this purpose has been
argued, in part, by analogy with DNA photolyase, although no
effects of applied magnetic fields have yet been reported for any
member of the cryptochrome/photolyase family. Here, we demonstrate
a magnetic-field effect on the photochemical yield of a
flavin–tryptophan radical pair in Escherichia coli photolyase. This
result provides a proof of principle that photolyases, and most
likely by extension also cryptochromes, have the fundamental
properties needed to form the basis of a magnetic compass.

S. J. Palmer, M. J. Rycroft and M. Cermack

Surv. Geophys., in press

Abstract

The possibility that conditions on the Sun and in the Earth's magnetosphere can affect human health at the Earth's surface has been debated for many decades. This work reviews the research undertaken in the field of heliobiology, focusing on the effect of the variations of geomagnetic activity on human cardiovascular health. Data from previous research are analysed for their statistical significance, resulting in support for some studies and the undermining of others. Three conclusions are the geomagnetic effects are more pronounced at higher magnetic latitudes, that extremely high as well as extremely low values of geomagnetic activity seem to have adverse health effects and that a subset of the population (10-15%) is predisposed to adverse health due to geomagnetic variations. The reported health effects of anthropogenic sources of electric and magnetic fields are also briefly discussed, as research performed in this area could help to explain the results from studies into natural electric and magnetic field interactions with the human body. Possible mechanisms by which variations in solar and geophysical parameters could effect human health are discussed and the most likely candidates investigated further. Direct effects of natural ELF electric and magnetic fields appear implausible; a mechanism involving some form of resonant absorption is more likely. The idea that the Schumann resonance signals could be the global environmental signal absorbed by the human body, thereby linking geomagnetic activity and human health is investigated. Suppression of melatonin secreted by the pineal gland, possibly via desynchronised biological rhythms, appears to be a promising contender linking geomagnetic activity and human health. There are indications that calcium ions in cells could play a role in one or more mechanisms. It is found to be unlikely that a single mechanism can explain all of the reported phenomena.